Method and device for allocating multi transmission timing to at least one timing advance group in a wireless access system for supporting carrier aggregation

ABSTRACT

The present invention relates to methods of allocating a Timing Advance (TA) value used for at least one timing advance group in a wireless access system for supporting carrier aggregation (CA). According to one embodiment of the present invention, a method of adjusting transmission timing for at least one TA group in a wireless access system for supporting CA includes: receiving, by a terminal, a physical downlink control channel (PDCCH) signal including a reserved bit indicating at least one TA group; receiving a medium access control (MAC) message including at least one TA value corresponding to at least one TA group; and transmitting an uplink signal by applying a TA value corresponding to a TA group in the TA group that the reserved bit indicates. At this point, each of the at least one TA group may include at least one primary cell.

TECHNICAL FIELD

The present invention relates to a wireless access system, and moreparticularly, to methods for allocating a plurality of Timing Advance(TA) values, methods for adjusting the transmission time of a radioframe using a TA value, and apparatuses supporting the same in awireless access system supporting Carrier Aggregation (CA).

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

DISCLOSURE Technical Problem

A Timing Advance (TA) transmission scheme refers to transmission of anuplink frame from a User Equipment (UE) earlier than the receptiontiming of a downlink frame, taking into account a propagation delaybetween a Base Station (BS) and the UE. Conventionally, TA is definedonly for a primary component carrier (i.e. a Primary Cell (PCell)).However, the conventional TA transmission scheme cannot be still used ina Carrier Aggregation (CA) environment where one or more carriers (i.e.serving cells) are aggregated.

An object of the present invention devised to solve the problem lies ona method for efficiently transmitting and receiving an uplink frame anda downlink frame.

Another object of the present invention is to provide a method fordefining one or more Timing Advance (TA) groups and allocating aplurality of TA/timing adjustment values to each TA group in a CAenvironment.

Another object of the present invention is to provide a method forenabling a UE to perform TA by transmitting a TA value for each servingcell, each TA group, or each inter-band to the UE in a CA environment.

Another object of the present invention is to provide a method forenabling a UE to perform TA on a serving cell or an inter-band bytransmitting a transmission timing difference to the UE in a CAenvironment.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The present invention provides methods for allocating a plurality ofTiming Advance (TA) values, methods for adjusting the transmission timeof a radio frame using a TA value, and apparatuses supporting the samein a wireless access system supporting Carrier Aggregation (CA).

The object of the present invention can be achieved by providing amethod for adjusting a transmission timing for at least one TimingAdvance (TA) group in a wireless access system supporting CarrierAggregation (CA), including receiving a Physical Downlink ControlChannel (PDCCH) signal including a reserved bit (i.e., a TA groupindicator) indicating at least one TA group, receiving a Medium AccessControl (MAC) message including at least one TA value for the at leastone TA group, and transmitting an uplink signal by applying the at leastone TA value to the at least one TA group indicated by the reserved bit.Each of the at least one TA group includes at least one Primary Cell(PCell).

In another aspect of the present invention, provided herein is a methodfor adjusting a transmission timing for at least one TA group in awireless access system supporting CA, including transmitting a PDCCHsignal including a reserved bit (i.e., a TA group indicator) indicatingat least one TA group, transmitting a MAC message including at least oneTA value for the at least one TA group, and receiving an uplink signalthat is transmitted by applying the at least one TA value to the atleast one TA group indicated by the reserved bit. Each of the at leastone TA group includes at least one PCell.

In another aspect of the present invention, provided herein is aterminal for adjusting a transmission timing for at least one TA groupin a wireless access system supporting CA, including a transmissionmodule, a reception module, and a processor configured to adjust thetransmission timing. The terminal receives a PDCCH signal including areserved bit (i.e., a TA group indicator) indicating at least one TAgroup through the reception module, receives a MAC message including atleast one TA value for the at least one TA group through the receptionmodule, and transmits an uplink signal by applying the at least one TAvalue to the at least one TA group indicated by the reserved bit throughthe processor. Each of the at least one TA group includes at least onePCell.

According to the aspect of the present invention, each of the at leastone TA group may have a different Uplink (UL)-Downlink (DL)configuration.

According to the aspect of the present invention, each of the at leastone PCell may have a different UL-DL configuration.

The at least one TA group may include a Secondary Cell (SCell) relatedto the at least one PCell. The at least one TA value may be appliedcommonly to one or more serving cells of the at least one TA groupcorresponding to the at least one TA value.

The afore-described aspects of the present invention are merely a partof preferred embodiments of the present invention. Those skilled in theart will derive and understand various embodiments reflecting thetechnical features of the present invention from the following detaileddescription of the present invention.

Advantageous Effects

According to the embodiments of the present invention, the followingeffects can be achieved.

First, a UE and a BS can efficiently transmit and receive an uplinkframe and a downlink frame.

Secondly, a UE can transmit an uplink radio frame accurately using a TAvalue for one or more TA groups even in a CA environment.

Thirdly, since multiple TA values are supported in an inter-band CAsituation, a UE can adjust the transmission time of an uplink radioframe.

Fourthly, a BS can receive an uplink signal without Inter-SymbolInterference (ISI) using multiple TA values even in a CA environment.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present invention;

FIG. 2 illustrates radio frame structures used in embodiments of thepresent invention;

FIG. 3 illustrates a structure of a DownLink (DL) resource grid for theduration of one DL slot, which may be used in embodiments of the presentinvention;

FIG. 4 illustrates a structure of an UpLink (UL) subframe, which may beused in embodiments of the present invention;

FIG. 5 illustrates a structure of a DL subframe, which may be used inembodiments of the present invention;

FIG. 6 illustrates an example of Component Carriers (CCs) and CarrierAggregation (CA) in a Long Term Evolution-Advanced (LTE-A) system, whichare used in embodiments of the present invention;

FIG. 7 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present invention;

FIG. 8 illustrates one of DL-UL timing relationships used in embodimentsof the present invention;

FIG. 9 illustrates an exemplary Timing Advance Command Medium AccessControl (TAC MAC) control element used in embodiments of the presentinvention;

FIG. 10 illustrates exemplary MAC Packet Data Unit (MAC PDU) subheadersused in embodiments of the present invention;

FIG. 11 illustrates an exemplary MAC Random Access Response (MAC RAR)used in embodiments of the present invention;

FIG. 12 illustrates an exemplary MAC PDU including a MAC header and MACRARs, which is used in embodiments of the present invention;

FIG. 13 illustrates a round trip delay taken into account for timingadjustment used in embodiments of the present invention;

FIG. 14 illustrates an exemplary DL-UL transmission timing based on aTiming Advance (TA) value, used in embodiments of the present invention;

FIG. 15 illustrates a case where the transmission timings of two or morecells configured for a User Equipment (UE) are aligned with each otheraccording to an embodiment of the present invention;

FIG. 16 illustrates a case where the transmission timings of two or morecells configured for a UE are not aligned with each other according toan embodiment of the present invention;

FIG. 17 illustrates methods for allocating a TA value using a DownlinkControl Information (DCI) format according to an embodiment of thepresent invention; and

FIG. 18 is a block diagram of apparatuses that may implement the methodsdescribed in FIGS. 1 to 17.

BEST MODE

Embodiments of the present invention relate to methods for allocating aTiming Advance (TA) value, methods for adjusting the transmission timeof a radio frame based on a TA value, and apparatuses supporting thesame in a wireless access system supporting Carrier Aggregation (CA).

The embodiments of the present invention described below arecombinations of elements and features of the present invention inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present invention may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present invention may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present invention will be avoided lestit should obscure the subject matter of the present invention. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

In the embodiments of the present invention, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present invention, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmitter is a fixed and/or mobile node that provides a data serviceor a voice service and a receiver is a fixed and/or mobile node thatreceives a data service or a voice service. Therefore, a UE may serve asa transmitter and a BS may serve as a receiver, on an UpLink (UL).Likewise, the UE may serve as a receiver and the BS may serve as atransmitter, on a DownLink (DL).

The embodiments of the present invention may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3^(rd) Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present invention may be supported bythe standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, and 3GPP TS 36.321. That is, the steps or parts, which are notdescribed to clearly reveal the technical idea of the present invention,in the embodiments of the present invention may be explained by theabove standard specifications. All terms used in the embodiments of thepresent invention may be explained by the standard specifications.

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present invention.

For example, the term used in embodiments of the present invention, TAis interchangeable with time advance, timing adjustment, or timeadjustment in the same meaning.

The embodiments of the present invention can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present invention are described in thecontext of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present invention, the present invention is alsoapplicable to an IEEE 802.16e/m system, etc.

1.3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general method using thephysical channels, which may be used in embodiments of the presentinvention.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a DL channel state by receiving a DownlinkReference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present invention.

FIG. 2( a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (T_(f)=307200·T_(s)) long, includingequal-sized 20 slots indexed from 0 to 19. Each slot is 0.5 ms(T_(siot)=15360·T_(s)) long. One subframe includes two successive slots.An i^(th) subframe includes 2i^(th) and (2i+1)^(th) slots. That is, aradio frame includes 10 subframes. A time required for transmitting onesubframe is defined as a Transmission Time Interval (TTI). T_(s) is asampling time given as T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns).One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols or SC-FDMA symbols in the time domain by aplurality of Resource Blocks (RBs) in the frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2( b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(T_(f)=307200·T_(s)) long, including two half-frames each having alength of 5 ms (=153600·T_(s)) long. Each half-frame includes fivesubframes each being lms (=30720·T_(s)) long. An i^(th) subframeincludes 2i^(th) and (2i+1)^(th) slots each having a length of 0.5 ms(T_(siot)=15360·T_(s)). T_(s) is a sampling time given as T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Normal Extended Normal Extended Special cycliccyclic cyclic cyclic subframe prefix in prefix in prefix in prefix inconfiguration DwPTS uplink uplink DwPTS uplink uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentinvention.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent invention is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, N_(DL)depends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present invention.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present invention.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

1.2 Physical Downlink Control Channel (PDCCH)

1.2.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a Downlink Shared Channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran Uplink Shared Channel (UL-SCH) (i.e. a UL grant), paging informationof a Paging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, Voice Over InternetProtocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel. ACCE includes a plurality of RE Groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.2.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by N_(REG). Then thenumber of CCEs available to the system is N_(CCE) (=└N_(REG)/9┘) and theCCEs are indexed from 0 to N_(CCE)−1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0.

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 PDCCH Number of Number of Number of format CCEs (n) REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or Modulation and Coding Scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format Resource grants for the PUSCHtransmissions (uplink) 0 Format Resource assignments for single codewordPDSCH trans- 1 missions (transmission modes 1, 2 and 7) Format Compactsignaling of resource assignments for single codeword 1A PDSCH (allmodes) Format Compact resource assignments for PDSCH using rank-1 closed1B loop precoding (mode 6) Format Very compact resource assignments forPDSCH (e.g. paging/ 1C broadcast system information) Format Compactresource assignments for PDSCH using multi-user 1D MIMO (mode 5) FormatResource assignments for PDSCH for closed-loop MIMO 2 operation (mode 4)Format Resource assignments for PDSCH for open-loop MIMO opera- 2A tion(mode 3) Format Power control commands for PUCCH and PUSCH with 2-bit/3/3A 1-bit power adjustment

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission ofTransmission Power Control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher-layer signaling(e.g. Radio Resource Control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically byhigher-layer signaling. For example, multi-antenna transmission schememay include transmit diversity, open-loop or closed-loop spatialmultiplexing, Multi-User Multiple Input Multiple Output (MU-MIMO), orbeamforming Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing theSignal to Interference plus Noise Ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 7 transmission modes are availableto UEs:

(1) Single antenna port: port 0;

(2) Transmit diversity;

(3) Open-loop spatial multiplexing;

(4) Closed-loop spatial multiplexing;

(5) MU-MIMO;

(6) Closed-loop rank-1 precoding; and

(7) Single antenna port: port 5.

1.2.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information. The CRC is masked by a unique Identifier (ID) (e.g.a Radio Network Temporary Identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a Paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a System Information Block(SIB), its CRC may be masked by a system information ID (e.g. a SystemInformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a Random Access-RNTI (RA-RNTI).

Then the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.2.4 Blind Decoding (BD)

A plurality of PDCCHs may be transmitted in a subframe. That is, thecontrol region of a subframe includes a plurality of CCEs, CCE 0 to CCEN_(CCE,k)−1. N_(CCE,k) is the total number of CCEs in the control regionof a k^(th) subframe. A UE monitors a plurality of PDCCHs in everysubframe. This means that the UE attempts to decode each PDCCH accordingto a monitored PDCCH format.

The eNB does not provide the UE with information about the position of aPDCCH directed to the UE in an allocated control region of a subframe.Without knowledge of the position, CCE aggregation level, or DCI formatof its PDCCH, the UE searches for its PDCCH by monitoring a set of PDCCHcandidates in the subframe in order to receive a control channel fromthe eNB. This is called blind decoding. Blind decoding is the process ofdemasking a CRC part with a UE ID, checking a CRC error, and determiningwhether a corresponding PDCCH is a control channel directed to a UE bythe UE.

The UE monitors a PDCCH in every subframe to receive data transmitted tothe UE in an active mode. In a Discontinuous Reception (DRX) mode, theUE wakes up in a monitoring interval of every DRX cycle and monitors aPDCCH in a subframe corresponding to the monitoring interval. ThePDCCH-monitored subframe is called a non-DRX subframe.

To receive its PDCCH, the UE should blind-decode all CCEs of the controlregion of the non-DRX subframe. Without knowledge of a transmitted PDCCHformat, the UE should decode all PDCCHs with all possible CCEaggregation levels until the UE succeeds in blind-decoding a PDCCH inevery non-DRX subframe. Since the UE does not know the number of CCEsused for its PDCCH, the UE should attempt detection with all possibleCCE aggregation levels until the UE succeeds in blind decoding of aPDCCH.

In the LTE system, the concept of Search Space (SS) is defined for blinddecoding of a UE. An SS is a set of PDCCH candidates that a UE willmonitor. The SS may have a different size for each PDCCH format. Thereare two types of SSs, Common Search Space (CSS) andUE-specific/Dedicated Search Space (USS).

While all UEs may know the size of a CSS, a USS may be configured foreach individual UE. Accordingly, a UE should monitor both a CSS and aUSS to decode a PDCCH. As a consequence, the UE performs up to 44 blinddecodings in one subframe, except for blind decodings based on differentCRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).

In view of the constraints of an SS, the eNB may not secure CCEresources to transmit PDCCHs to all intended UEs in a given subframe.This situation occurs because the remaining resources except forallocated CCEs may not be included in an SS for a specific UE. Tominimize this obstacle that may continue in the next subframe, aUE-specific hopping sequence may apply to the starting point of a USS.

[Table 4] illustrates the sizes of CSSs and USSs.

TABLE 4 Number of Number of PDCCH Number of candidates in candidates informat CCEs (n) common search space dedicated search space 0 1 — 6 1 2 —6 2 4 4 2 3 8 2 2

To mitigate the load of the UE caused by the number of blind decodingattempts, the UE does not search for all defined DCI formatssimultaneously. Specifically, the UE always searches for DCI Format 0and DCI Format 1A in a USS. Although DCI Format 0 and DCI Format 1A areof the same size, the UE may distinguish the DCI formats by a flag forformat0/format 1a differentiation included in a PDCCH. Other DCI formatsthan DCI Format 0 and DCI Format 1A, such as DCI Format 1, DCI Format1B, and DCI Format 2 may be required for the UE.

The UE may search for DCI Format 1A and DCI Format 1C in a CSS. The UEmay also be configured to search for DCI Format 3 or 3A in the CSS.Although DCI Format 3 and DCI Format 3A have the same size as DCI Format0 and DCI Format 1A, the UE may distinguish the DCI formats by a CRCscrambled with an ID other than a UE-specific ID.

An SS S_(k) ^((L)) is a PDCCH candidate set with a CCE aggregation levelLε{1, 2, 4, 8} The CCEs of PDCCH candidate set m in the SS may bedetermined by the following equation.

L·{(Y _(k) +m)mod└N _(CCE,k) /L┘}+i  [Equation 1]

where M^((L)) is the number of PDCCH candidates with CCE aggregationlevel L to be monitored in the SS, m=0 . . . , M^((L))−1, i is the indexof a CCE in each PDCCH candidate, and i=0, . . . , L−1. k=└n_(s)/2┘where n_(s) is the index of a slot in a radio frame.

As described before, the UE monitors both the USS and the CSS to decodea PDCCH. The CSS supports PDCCHs with CCE aggregation levels {4, 8} andthe USS supports PDCCHs with CCE aggregation levels {1, 2, 4, 8}. [Table5] illustrates PDCCH candidates monitored by a UE.

TABLE 5 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1 6 6 specific 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

Referring to [Equation 1], for two aggregation levels, L=4 and L=8,Y_(k) is set to 0 in the CSS, whereas Y_(k) is defined by [Equation 2]for aggregation level L in the USS.

Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

where Y₋₁=n_(RNTI)≠0, n_(RNTI) indicating an RNTI value. A=39827 andD=65537.

2. Carrier Aggregation (CA) Environment

2.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present invention, multi-carrier means CA (or carrier combining).Herein, CA covers aggregation of contiguous carriers and aggregation ofnon-contiguous carriers. The number of aggregated CCs may be differentfor a DL and a UL. If the number of DL CCs is equal to the number of ULCCs, this is called symmetric aggregation. If the number of DL CCs isdifferent from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent invention may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCe11)are defined. A PCell and an SCe11 may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present invention.

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present invention.

FIG. 6( a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 6( b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 6( b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≦N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≦M≦N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

2.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher-layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a Carrier Indicator Field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set ispreferably defined within the UE DL CC set. That is, the eNB transmits aPDCCH only in the PDCCH monitoring set to schedule a PDSCH or PUSCH forthe UE.

FIG. 7 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present invention.

Referring to FIG. 7, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher-layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC ‘C’ that are not configured as PDCCHmonitoring DL CCs.

3. Overview of UL/DL Scheduling in TDD System

3.1 UL-DL Configurations in TDD System

UL-DL configurations for frame structure type 2 represent rules ofallocating (or reserving) each subframe as a DL subframe or a ULsubframe. [Table 6] lists such UL-DL configurations.

TABLE 6 Uplink- Downlink- downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 5 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6 5 ms D S U U U D S U U D

Referring to [Table 6], “D” represents a DL subframe, “U” represents aUL subframe, and “S” represents a special subframe including a DwPTS, aGP, and an UpPTS in a radio frame. 7 UL-DL configurations are availableand differ in the positions or numbers of DL subframes, specialsubframes, and UL subframes.

A time point at which DL switches to UL or UL switches to DL is called aswitch point. Switch-point periodicity is a period in which switchingbetween a UL subframe and a DL subframe is repeated in the same manner.The switch-point periodicity is 5 ms or 10 ms. If the switch-pointperiodicity is 5 ms, a special subframe S exists in every half-frame andif the switch-point periodicity is 10 ms, a special subframe S isconfined to the first half-frame.

In every UL-DL configuration, subframe 0, subframe 5, and the DwPTS areused for DL transmission, and the UpPTS and the subframe following aspecial subframe are always used for UL transmission.

The UL-DL configurations are system information that may be known toboth an eNB and UEs. Each time UL-DL configuration information ischanged, the eNB may indicate the change in the UL-DL allocation stateof a radio frame to a UE by transmitting only the index of configurationinformation. The configuration information is a kind of DCI and may betransmitted on a DL control channel, PDCCH like other schedulinginformation. The configuration information may be broadcast to all UEswithin a cell on a BCH. The number of half-frames in a radio frame, thenumber of subframes in a half-frame, and DL-UL subframe combinations inthe TDD system are purely exemplary.

3.2. UL/DL Scheduling in TDD System

A DL/UL subframe configuration is different according to a UL-DLconfiguration in the TDD system. Therefore, the transmission timings ofa PUSCH and a PHICH are different according to a UL-DL configuration.The transmission timings of a PUSCH and a PHICH may be differentaccording to the index (or number) of a subframe.

In the LTE system, a UL/DL timing relationship among a PUSCH, a PDCCHthat schedules the PUSCH, and a PHICH that carries a DL HARQ ACK/NACKfor the PUSCH is preset.

[Table 7] illustrates the transmission timings of a PDCCH and a PUSCHassociated with the PDCCH for each UL-DL configuration.

TABLE 7 TDD UL/DL subframe number n Configuration 0 1 2 3 4 5 6 7 8 9 04 6 4 6 1 6 4 6 4 2 4 4 3 4 4 4 4 4 4 5 4 6 7 7 7 7 5

Referring to [Table 7], in UL-DL configuration 1 to UL-DL configuration6, for retransmission after receiving a UL grant on a PDCCH or receivinga PHICH from an eNB in an n^(th) DL subframe, the UE transmits a PUSCHin an (n+k)^(th) UL subframe according to the index of the DL subframecarrying the PDCCH (or the PHICH). Herein, k values are listed in [Table7].

In the case of UL-DL configuration 0, a PUSCH is transmitted in a ULsubframe indicated by [Table 7], in an (n+7)^(th) UL subframe, or both,according to UL indexes set in a UL DCI format, the index of a DLsubframe carrying a PHICH, and I_(PHICH) received by higher-layersignaling or determined by the index of a UL subframe carrying a PUSCH.

4. UL-DL Frame Timing

FIG. 8 illustrates one of UL-DUL timing relationships used inembodiments of the present invention.

Referring to FIG. 8, a UE starts to transmit UL radio frame i(N_(TA)+N_(TA onset))×T_(s) seconds (0≦N_(TA)≦20512) before acorresponding DL radio frame is transmitted. N_(TA offset)=0 in framestructure type 1 and N_(TA offset)=624 in frame structure type 2 inFIG. 1. However, all slots of the radio frame are not transmitted. Forexample, only a part of the slots of the radio frame is transmitted inthe TDD system.

Upon receipt of a Timing Advance Command (TAC), the UE adjusts the ULtransmission timing of a PUCCH/PUSCH/SRS in a PCell. The TAC indicatesthe amount of UL timing adjustment for a current UL timing, which is amultiple of 16T_(s). The UL transmission timing of a PUSCH/SRS in anSCell is identical to the UL transmission timing of a PUSCH/SRS in thePCell.

In the case of a random access response, a 11-bit TAC is an index T_(A)(e.g. T_(A)=0, 1, 2, . . . , 1282) from which N_(TA) is determined. TheTA value for timing adjustment, N_(TA) is given as T_(A×)16. In anothercase, a 6-bit TAC indicates a T_(A) value, that is, an adjustment valuefor a current TA value N_(TA, old) to get a new TA value N_(TA,new). Forexample, N_(TA,new)=N_(TA,old)+(T_(A)−31)×16. The adjustment valueN_(TA) is positive-signed or negative-signed, indicating advance ordelay of a UL transmission timing by a given value.

Regarding a TAC received in subframe n, timing adjustment starts fromsubframe n+6 based on the TAC. If the timing adjustment leads to overlapbetween PUCCH/PUSCH/SRS transmissions in subframe n and n+1, the UEtransmits the whole subframe n, without the overlapped part of subframen+1. If a DL reception timing is changed without a TAC and not correctedor partially corrected by UL timing adjustment, the UE changes N_(TA).

4.1 TAC MAC Control Element

FIG. 9 illustrates an exemplary Timing Advance Command Medium AccessControl (TAC MAC) control element used in embodiments of the presentinvention.

The TAC MAC control element is defined by a MAC PDU subheader with aLogical Channel ID (LCID). [Table 8] illustrates exemplary LCIDs.

TABLE 8 Index LCID values 00000 CCCH 00001-01010 Identify of the logicalchannel 01011-11010 Reserved 11011 Activation/Deactivation 11100 UEContention Resolution Identity 11101 Timing Advance Command 11110 DRXCommand 11111 Padding

In FIG. 9, the TAC MAC control element includes two R fields and a TACfield. Each of the R fields is set to ‘0’ as a reserved bit and the TACfield indicates an index T_(A) used for a UE to control the amount oftiming adjustment.

FIG. 10 illustrates exemplary MAC subheaders used in embodiments of thepresent invention.

In the embodiments of the present invention, a MAC PDU includes a MACheader, zero or more MAC Random Access Response (RAR) fields, and anoptional padding. A MAC RAR field indicates a MAC header having avariable value for a random access response and includes zero or moreMAC PDU subheaders. Each MAC PDU subheader except for a BackoffIndicator subheader corresponds to a MAC RAR. If the Backoff Indicatorsubheader is included, it is included only once, as the first subheaderof the MAC PDU header.

Referring to FIG. 10( a), a MAC PDU subheader includes three headerfields E/T/RAPID. Referring to FIG. 10( b), the Backoff Indicatorsubheader includes five header fields E/T/R/R/BI.

E is an extension field indicating whether more fields are present in acorresponding MAC header. For example, the E field indicates whether atleast one another field follows the E/T/RAPID field.

T is a type field indicating whether the MAC subheader contains a randomaccess ID or a Backoff Indicator (BI). For example, the T field is setto ‘0’ to indicate the presence of a BI field in the subheader and to‘1’ to indicate the presence of a Random Access Preamble ID (RAPID)field.

BI is a Backoff Indicator field that identifies the overload conditionof a corresponding cell. The size of the BI field is 4 bits. The RAPIDfield identifies a transmitted random access preamble. The size of theRAPID field is 6 bits.

FIG. 11 illustrates an exemplary MAC RAR used in embodiments of thepresent invention.

Referring to FIG. 11, the MAC RAR includes four fields, R/TAC/ULGrant/Temporary C-RNTI. The MAC RAR may be padded with bits at its end.The presence and length of the padding bits may be determined implicitlybased on a Transport Block (TB) size, the number of RARs, and the sizeof a MAC header.

FIG. 12 illustrates an exemplary MAC PDU including a MAC header and MACRARs, which is used in embodiments of the present invention.

Referring to FIG. 12, the MAC PDU includes a MAC header, zero or moreMAC RARs, and optional padding bits. The zero or more MAC RARs may makeup MAC payload. The MAC header includes one or more MAC PDU subheaders.FIG. 10 may be referred to for these MAC PDU subheaders.

FIG. 13 illustrates a round trip delay taken into account for timingadjustment used in embodiments of the present invention.

In the LTE/LTE-A system, an eNB transmits a TA message to a UE to setthe starting point of a UL signal transmitted by the UE, taking intoaccount the position of the UE and the propagation characteristics of afrequency band.

A TA value transmitted by the eNB may be represented by a Round TripDelay (RTD). For example, the TA value is determined to be the sum of ULand DL propagation delays plus a maximum channel impulse response delay.That is, the TA value is intended for the eNB to receive and decode ULsignals from UEs at the same timing, in consideration of the positionsof the UEs and the propagation characteristics of frequency bands. Thus,the UEs transmit UL radio frames in FDD (frame structure type 1) and TDD(frame structure type 2) by advancing the transmission starting pointsof the UL radio frames by TA values. A related embodiment has beendescribed before with reference to FIG. 8. 0≦N_(TA)≦20512 whereN_(TA offset)=0 in FDD and N_(TA offset)=624 in TDD.

FIG. 14 illustrates an exemplary DL/UL transmission timing based on a TAvalue, used in embodiments of the present invention.

Referring to FIG. 14, an eNB transmits a DL radio frame to each UE instage 1. As long a transmission delay as a DL signal propagation delayoccurs due to the position of the UE and the propagation characteristicsof a frequency band. If the RTDs of UE1 and UE2 are set to N_(TA1) andN_(TA2), respectively, UE1 and UE2 have DL signal propagation delays ofN_(TA1)/2 and N_(TA2)/2 and UL signal propagation delays of N_(TA1)/2and N_(TA2)/2, respectively.

The UEs transmit UL radio frames by advancing the transmission startingtimings of the UL radio frames by N_(TA1) and N_(TA2), respectively withrespect to received DL radio frames, and the transmitted UL radio framesexperience the UL propagation delays of N_(TA1)/2 and N_(TA2)/2,respectively in stage 2. Consequently, the timing advances of N_(TA1)and N_(TA2) of the UL radio frames are counterbalanced with the sums ofthe DL and UL propagation delays and thus the eNB may receive the ULradio frames with their starting points aligned from the UEs in stage 3.

There are two types of CA, intra-band CA and inter-band CA. Inintra-band CA, cells configured for a UE have adjacent band frequencies(i.e. intra-bands), whereas in inter-band CA, cells configured for a UEhave frequencies far from each other (i.e. inter-bands).

In intra-band CA, since cells configured for a UE have similar frequencyband characteristics, an RTD caused by the position of the UE and thepropagation characteristics of a frequency band may not be differentmuch between the cells. In contrast, the cells may have significantlydifferent frequency band characteristics in inter-band CA. That is,since the cells differ in propagation characteristics such as thepropagation range of a signal or diffraction property, a different TA ispreferably allocated to each cell in inter-band CA.

FIG. 15 illustrates a case where the transmission timings of two or morecells configured for a UE are aligned with each other according to anembodiment of the present invention.

Referring to FIG. 15, with two cells (e.g. a PCell and an SCell)configured for a UE, the reception timings of radio frames in the twocells transmitted by an eNB are aligned at the UE. Herein, t1 representsthe DL propagation delay of the PCell and t2 represents the receptiontiming difference between the PCell and the SCell. t2 may be measuredusing a synchronization signal or an RS.

While the starting timings of the radio frames transmitted in the cellsare aligned, the radio frames experience propagation delays due to thepropagation characteristics of the cells. Since the eNB transmits a TAvalue for the PCell to the UE in a conventional wireless access system,the UE may receive a TA value twice as large as t1 from the eNB by a MACmessage.

The UE may determine a TA value for the SCell by t1+t2. That is, the UEmay calculate the TA value for the SCell by summing the TA value for thePCell and the reception timing difference acquired using a DLsynchronization signal (or RS) of the PCell and a DL synchronizationsignal (or RS) of the SCell. However, if the transmission timings of DLframes in cells transmitted by the eNB are not aligned, the UE may notcalculate a TA value in the same manner as described with reference toFIG. 15.

FIG. 16 illustrates a case where the transmission timings of two or morecells configured for a UE are not aligned with each other according toan embodiment of the present invention.

When an eNB transmits radio frames in two or more cells to a UE, thetransmission starting timings of the radio frames may not be aligned.These radio frames also experience their respective DL propagationdelays.

Herein, t1 represents a DL propagation delay of a PCell and t2represents the reception timing difference between the PCell and anSCell. The UE may acquire the reception timing difference t2 using a TAvalue for the PCell and a synchronization signal or RS of the PCell.However, the UE may not calculate a TA value for the SCell (i.e. t2+xvalue) in the illustrated case of FIG. 16. This is because although theTA value for the SCell may be represented as t2+x value, the UE may notacquire information about the x value because of the differenttransmission starting timings of the PCell and the SCell.

Especially in the afore-described inter-band CA (or inter-band multi-CA)environment, it is difficult to align the transmission timings ofsignals in cells. Since the cells differ in frequency bandcharacteristics, different RF devices are used according to thefrequency bands of the cells and have different non-linearcharacteristics and different time delays due to the different frequencybands.

The constraint that the transmission timings of signals in cells shouldbe aligned may become severe to the eNB and the network in theinter-band CA environment because misalignment between the transmissiontimings of DL signals in cells may not be avoided.

Moreover, a TA is defined only for a PCell in a legacy system. Since oneor more SCells are configured in addition to an existing PCell for a UEin a CA environment, the conventional TA transmission scheme based on aPCell may not still be used for an SCell.

4.2 Method for Allocating TA Value

To overcome the above problem, it is preferred that an eNB allocates aTA value to each of cells operating in inter-bands in inter-band CA.Accordingly, a description will be given below of methods for allowing aUE to perform a TA operation on each cell by transmitting a TA value foreach cell to the UE by an eNB, in the case where two or more cells areconfigured for the UE.

If all of the two or more cells are configured in inter-bands, the UEmay need TA values for all cells. If one or more cells are grouped intoone group and thus one band, as many TA values as the number of bandsmay be required. In embodiments of the present invention, TA valuesrequired for a UE are referred to as multiple TAs.

In embodiments of the present invention, a current TA value istransmitted to a UE by a MAC message. The MAC message may be configureddifferently for an RAR or tracking. For example, a TA value allocatedfor an RAR may be 11 bits and a TA value allocated for tracking may be 6bits.

4.2.1 Methods for Allocating TA Value on TA Group Basis

A TA group is a set of serving cells having UL resources sharing thesame TA value. The TA group may include one or more serving cells. AneNB determines the relationship between configured CCs and TA groups. Inthe present invention, a TA group maintenance mechanism for a PCell anda TA group may be applied in the same manner as the legacy LTE-A system.A TA group may be managed cell-specifically or UE-specifically and atleast two TA groups may be allocated to a UE.

In embodiments of the present invention, one or more cells may begrouped and a TA value may be allocated on a group basis. For example, aUE may transmit a UL signal to an eNB by applying the same TA value tocells of a specific group. In addition, the eNB may transmit the same TAvalue for a TA group, instead of transmitting a TA value for each cellto each UE, thereby reducing the transmission overhead of TA messagestransmitted to allocate a TA value to each UE.

In embodiments of the present invention, one or more TA groups may beallocated to one UE, one TA group may include one or more serving cells,and one TA group may include one or more PCells. Accordingly, as many TAvalues as the number of allocated TA groups may be allocated to the UE.

A TA group may include one or more serving cells. Then the TA group maybe configured according to the frequency bands of the serving cells. Inaddition, the eNB may configure multiple TA groups (i.e. multiple cellgroups) for a specific UE.

If a UE receives multiple TA values for multiple TA groups, the UE maytransmit a UL signal by applying the same TA to the serving cells ofeach TA group (or cell group). Cells carrying multiple TA values (or areference cell of each group) may be multiple PCells. Or cells carryingmultiple TA values may be serving cells selected by higher-layersignaling, serving cells transmitting an RACH signal, or specificserving cells that transmit a PDCCH order indicating transmission of adedicated RACH preamble. In embodiments of the present invention, aserving cell carrying a TA value or a reference serving cell of each TAgroup is defined as a PCell, for the convenience of description.

Compared to the legacy LTE-A system (conforming to Rel-10) in which onlyone PCell is configured for one UE, multiple PCells may be used formultiple TA groups (or multiple cell groups). That is, one UE may haveone or more PCells (or cell groups) and may feed back an ACK/NACK signalor CSI in a PUCCH region of each PCell.

The number of PCells available to a UE may be equal to or smaller thanthe total number of serving cells configured for the UE. Herein, UCI maybe transmitted on a PUCCH and/or PUSCH of each PCell in a method definedby the legacy LTE-A system.

Now a detailed description will be given of various methods for usingone or more PCells (or cell groups) by a UE and methods for configuringcell groups. A cell group may be used to configure a TA group and cellgroups each including one or more serving cells may be mapped to TAgroups in a one-to-one, multi-to-one, or one-to-multi correspondence.

4.2.1.1 Cell Group Configuration Method 1

One or more PCells may be allocated to a UE. The number of PCellsallocated to the UE may be preset by a network system or indicated byhigher-layer signaling. For example, the number of PCells allocated tothe UE may be determined based on the number of serving cells orinter-bands configured for the UE. In the case of multiple PCells, thePCells may have different UL-DL configurations.

In the present invention, multiple PCells are configured in thefollowing cases. (1) One PCell and one or more SCells may be configuredin UL CCs, whereas one or more PCells and one or more SCells may beconfigured in DL CCs. Or (2) One PCell and one or more SCells may beconfigured in DL CCs, whereas one or more PCells and one or more SCellsmay be configured in UL CCs. Or (3) one or more PCells and one or moreSCells may be configured in both DL CCs and UL CCs.

The UE may have one or more SCells related to each PCell. Obviously, aspecific PCell may be related to no SCell. If a reference cell in whichthe UE transmits a UCI feedback for serving cells configured for the UEis defined as a PCell, one or more SCells related to a PCell refer toserving cells grouped with the PCell.

For a criterion for transmitting a UCI feedback for serving cells,“Table 10.1-1: Downlink association set index K: {k₀, k₁, . . . ,k_(M-1)} for TDD” of TS 36.213 v10.0.1 for LTE-A may be referred to. APCell may mean a serving cell being a reference for applying the size ofbundling windows, M related to Table 10.1-1 and/or a serving cell havinga PUCCH.

The UE may feed back UCI about a PCell and SCells related to the PCellon one PUCCH to the eNB. The PCell and its related SCells may be locatedin the same band (e.g., potentially the same Radio Frequency (RF) band).If a specific PCell and one or more related SCells form one cell group(e.g., one TA group), all cells of the cell group have the same UL-DLconfiguration.

In the present invention, a cell group is formed or configured in alogical sense, and thus not in a physical sense. In the absence of anySCell related to a PCell, a TA group may include only the PCell.Therefore, the UE may have one or more TA groups and each TA group mayinclude one PCell. In the presence of an SCell related to a PCell, theTA group of the PCell may include the related SCell.

For one or more cell groups, the UE may transmit an ACK/NACK feedback,report CSI, and/or transmit a sounding signal on a PUCCH of a PCellincluded in each cell group. Because the same DL-UL configuration is setfor cells of each cell group, the afore-described conventional problemdoes not occur in the cell group. However, different cell groups mayneed different RF ends.

In the foregoing embodiments of the present invention, the cells of thesame cell group may be configured in intra-band CA and cell groups maybe configured in inter-band CA. For example, a part of cells configuredin inter-band CA may form different cell groups and the other part ofthe cells may form another cell group. Herein, the number of PCellsavailable to a specific UE may be equal to or smaller than the totalnumber of inter-bands configured for the UE.

4.2.1.2 Cell Group Configuration Method 2

In an embodiment of the present invention described below, a UE maysupport only a predetermined number of or fewer UL-DL configurations.The predetermined number x (e.g. 2) of UL-DL configurations may bepreset by a network system or indicated to the UE by higher-layersignaling. The x UL-DL configurations may be preset according to thenumber of serving cells or inter-bands configured for the UE. The sameor different UL-DL configurations may be applied to all UEs.

The eNB may configure serving cells for the UE using x or fewerdifferent UL-DL configurations. For example, if x is 2 commonly to allUEs, the eNB may configure serving cells using only two different UL-DLconfigurations.

The serving cells configured by the eNB may be allocated or indicated tothe UE. While each serving cell of a cell group (e.g., a TA group) mayhave a different UL-DL configuration, the cell group may be limited to xor fewer different UL-DL configurations.

The UE may group cells having the same UL-DL configuration into the samegroup from among the serving cells configured by the eNB. In this case,because only x or fewer UL-DL configurations are allocated to the UE, xor fewer cell groups may be formed. The formation/configuration of acell group may be viewed from a logical perspective and thus a physicalcell group may not be created actually. That is, a cell group has adifferent UL-DL configuration and includes one or more serving cells.

In the present invention, one specific serving cell per cell group maybe set as a PCell. The eNB may indicate the PCells to the UE byhigher-layer signaling. Or the UE may set the PCells in a predeterminedrule. For example, a serving cell having the lowest cell ID in each cellgroup may be set as a PCell of the cell group.

In regards to one or more cell groups, the UE may transmit an ACK/NACKfeedback, report CSI, and/or transmit a sounding signal on a PUCCH of aPCell included in each cell group. Because the same DL-UL configurationis set for cells of each cell group, the afore-described conventionalproblem does not occur in the cell group. However, different cell groupsmay need different RF ends.

In the foregoing embodiments of the present invention, the cells of thesame cell group may be configured in intra-band CA and cell groups maybe configured in inter-band CA. For example, a part of cells ofinter-band CA may form different cell groups and the other part of thecells may form another cell group. Herein, the number of PCellsavailable to a specific UE may be equal to or smaller than the totalnumber of inter-bands configured for the UE.

4.2.2 Methods for Allocating TA Value Using DCI Format

Now, methods for allocating a TA value using the TA group-based TAallocation method described in Clause 4.2.1 will be described in detail.

FIG. 17 illustrates methods for allocating a TA value using a DCI formataccording to an embodiment of the present invention.

Referring to FIG. 17, an eNB may indicate a serving cell (or a TA group)to which a TA value set in a MAC message is to be applied, usingreserved bits of a DCI format of a PDCCH (S1710).

For example, the eNB may indicate a TA value using an HARQ processnumber field or a DL assignment index field (only in TDD) as reservedbits of DCI Format 1A or using reserved bits padded to DCI Format 1C(i.e. a serving cell or a TA group to which a TA value will be appliedmay be indicated). The reserved bits may be used as a serving cellindicator indicating a specific serving cell. Since one or more TAgroups may be allocated to a UE as described before, one or more TAvalues for each group may be indicated to the UE.

In FDD, the HARQ process number field may be 3 bits to indicate acurrent HARQ process out of a maximum number (8) of HARQ processes. InTDD, the HARQ process number field may be 4 bits to indicate a currentHARQ process out of a maximum number (15) of HARQ processes, asillustrated in [Table 9]. [Table 9] lists maximum numbers of HARQprocesses according to UL/DL configurations.

TABLE 9 TDD UL/DL Configuration Maximum HARQ process number 0 4 1 7 2 103 9 4 12 5 15 6 6

However, if the CRC of DCI format 1A is scrambled or masked with anRA-RNTI, a P-RNTI, or an SI-RNTI, the HARQ process number field is usedas a reserved value. Therefore, the HARQ process number field may beused as TA identification information or TA indication information.

With continued reference to S1710 of FIG. 17, the eNB may indicate aband or a cell to which the TA value set in the MAC message is appliedfrom among two or more cells configured for the UE by scrambling the CRCof DCI format 1A with an RA-RNTI, a P-RNTI, or an SI-RNTI and thus usingthe HARQ process number field as reserved bits. That is, the TA valueset in the MAC message is not fixed as a TA value for a PCell. Rather,the TA value set in the MAC message may apply to a serving cell or bandindicated by the HARQ process number field from among a plurality ofserving cells.

For example, if the eNB configures the HARQ process number field of DCIFormat 1A for a UE having five configured cells in FDD as illustrated in[Table 10] and transmits the HARQ process number field to the UE, the UEmay determine and identify a cell to which a TA value received in a MACmessage is to be applied, from the HARQ process number field. In TDD,the HARQ process number field is 4 bits, which may be configured byadding ‘0’ to the start of the bits listed in [Table 10].

[Table 10] illustrates an exemplary HARQ process number field.

TABLE 10 HARQ process Serving cell index number field bits(ServCellIndex) 0 000 1 1 001 2 2 010 3 3 011 4 4 100 5 5 101 6 6 110 77 111 8

Referring to [Table 10], if the HARQ process number field is set to 3,the UE may determine that a TA value included in a MAC message appliesto a serving cell having serving cell index 4. The mapping relationshipbetween the HARQ process number field and the ServCellIndex field ispurely exemplary and thus may be configured differently or as adifferent table. To support multiple TAs, the eNB may indicate a newmapping table or mapping method between the HARQ process number fieldand the ServCellIndex field to the UE by RRC signaling (not shown).

If the CRC of DCI format 1A with the HARQ process number field in [Table9] is scrambled or masked with an RA-RNTI, a P-RNTI, or an SI-RNI, theHARQ process number field is used as a reserved value, as describedbefore. Herein, the HARQ process number field may be used as TAidentification information or TA indication information. For example, ifthe HARQ process number field is used as a reserved value, the HARQprocess number field may indicate a TA group requiring TA adjustmentfrom among one or more TA groups allocated to the UE.

Referring to FIG. 17 again, the eNB may transmit one or more TA valuesfor serving cells or TA groups to the UE by MAC messages describedbefore with reference to FIGS. 9, 10, and 11 (S1720).

The UE may determine that the TA value received in step S1720 is for theserving cell (or the TA group) indicated by the reserved value of theDCI format of the PDCCH received in step S1710 and thus may determinethe transmission timing of a radio frame to be transmitted in theserving cell (or the TA group). Thus, the UE may transmit a UL frame/ULsignal to the eNB by reflecting the TA value in the indicated servingcell (or TA group) (S1730).

In another method, the eNB may allocate a TA value to the UE by groupingone or more serving cells. For example, if one or more serving cells aregrouped, the one or more serving cells form one band. In step S1710, thereserved value may indicate at least one band. In this case, the UE maydetermine that the TA value included in the MAC message is for theindicated band and may transmit UL radio frames to the eNB by applyingthe TA value to the serving cells of the band (refer to Clause 4.2.1).

In another method, the eNB and the UE may apply the existing mappingrelationship between a CIF and a serving cell index field indicated byRRC signaling as the mapping relationship between an HARQ process numberfield and a serving cell index field in FIG. 17.

4.2.3 Method for Allocating TA Value Using CIF

If a CIF is configured in a DCI format, an eNB may indicate to a UE thata TA value set in a MAC message applies to a serving cell indicated bythe CIF.

For example, the eNB may indicate a mapping relationship between CIFsand serving cell indexes to the UE by RRC signaling (not shown). In thiscase, a CIF included in the PDCCH signal received in step S1710indicates a specific serving cell (or TA group) according to the mappingrelationship indicated by RRC signaling. If the UE receives a MACmessage including a TA value in step S1720, the UE may transmit a ULframe/UL signal by applying the TA value to the serving cell (or TAgroup) indicated by the CIF in step S1730.

While the eNB and the UE may still use the existing mapping relationshipbetween CIFs and serving cell indexes indicated by RRC signaling, theeNB may indicate a new mapping table or mapping relationship betweenCIFs and serving cell indexes to the UE in order to support multipleTAs.

4.2.4 Method for Allocating TA Value Using MAC Message

An eNB may transmit multiple TA values to a UE by aggregating MACmessages so that the UE may adjust the transmission timings of UL radioframes.

For example, the eNB may aggregate as many MAC messages as the number nof serving cells (or TA groups) configured for the UE. The payload sizeof the aggregated MAC message may be n times larger than the payloadsize of an existing MAC message including a TA value only for a PCell.

Or the eNB may aggregate as many MAC messages as the number m ofinter-bands, instead of MAC messages for all serving cells configuredfor the UE. Herein, inter-bands refer to multi-inter-band CA in whichone or more serving cells are aggregated. One or more inter-bands may beconfigured for the UE. In this case, the payload size of the MAC messagemay be m times larger than the payload size of the existing MAC messageincluding a TA value only for a PCell and the UE may apply the same TAvalue to one or more serving cells (or TA groups) belonging to the sameinter-band. That is, the UE may determine the transmission timings of ULradio frames by applying the same TA value to the serving cells (or TAgroups) of the same inter-band.

4.2.5 Method for Allocating Transmission Timing Difference between RadioFrames

An eNB may transmit a transmission timing difference between radioframes transmitted in serving cells (or TA groups) to a UE. For example,if two serving cells (or TA groups) are configured for the UE asillustrated in FIG. 16, the transmission timing difference y between aPCell and an SCell may be represented as t1−x. In this case, the UE maycalculate a TA value (i.e. x+t2) for the SCell to be t1−y+t2.

4.2.5.1 Method for Using Higher-Layer Signaling

An eNB may transmit a transmission timing difference y to a UE byhigher-layer signaling. For example, the higher-layer signaling may beRRC signaling or MAC signaling.

The value of y may include the transmission timing difference between aPCell and each SCell.

Or the transmitting timing difference y may include sequentialtransmission timing differences between serving cell indexes.

Or the eNB may transmit a transmission timing difference for aninter-band to the UE, instead of transmission timing differences for allserving cells (or TA groups).

4.2.5.2 Method for Using PDCCH Signal

An eNB may transmit a transmission timing difference y to a UE bypredetermined bits of a DCI format. For example, the reserved bits of aDCI format described before with reference to FIG. 17 may be used. Inthis case, the method described in Clause 4.2.1 or 4.2.2 may be used asa method for setting reserved bits of a DCI format.

Herein, the value of y may include the transmission timing differencebetween a PCell and each SCell.

Or the transmitting timing difference y may include sequentialtransmission timing differences between serving cell indexes.

Or the eNB may transmit a transmission timing difference for aninter-band to the UE, instead of transmission timing differences for allserving cells.

5. Apparatuses

Apparatuses illustrated in FIG. 18 are means that can implement themethods described before with reference to FIGS. 1 to 17.

A UE may act as a transmitter on a UL and as a receiver on a DL. A BSmay act as a receiver on a UL and as a transmitter on a DL.

That is, each of the UE and the BS may include a Transmission (Tx)module 1840 or 1850 and a Reception (Rx) module 1860 or 1870, forcontrolling transmission and reception of information, data, and/ormessages, and an antenna 1800 or 1810 for transmitting and receivinginformation, data, and/or messages.

Each of the UE and the BS may further include a processor 1820 or 1830for implementing the afore-described embodiments of the presentinvention and a memory 1880 or 1890 for temporarily or permanentlystoring operations of the processor 1820 or 1830.

The embodiments of the present invention may be performed using thecomponents and functions of the UE and the BS. For example, theprocessor of the BS may allocate and transmit a TA value or atransmission timing difference y to the UE by combining the methodsdisclosed in Clause 1 to Clause 4. The processor of the UE may adjustthe timings of one or more serving cells based on the TA value or the yvalue. For details, refer to Clause 1 to Clause 4.

The Tx and Rx modules of the UE and the BS may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDMA packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the BS of FIG. 18may further include a low-power Radio Frequency (RF)/IntermediateFrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present invention may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present invention may be implemented in the form of amodule, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory1880 or 1890 and executed by the processor 1820 or 1830. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentinvention or included as a new claim by a subsequent amendment after theapplication is filed.

INDUSTRIAL APPLICABILITY

Embodiments of the present invention are applicable to various wirelessaccess systems including a 3GPP system, a 3GPP2 system, and/or an IEEE802.xx system. In addition to these wireless access systems, theembodiments of the present invention are applicable to all technicalfields in which the wireless access systems find their applications.

1. A method for adjusting a transmission timing for at least one TimingAdvance (TA) group in a wireless access system supporting CarrierAggregation (CA), the method comprising: receiving a Physical DownlinkControl Channel (PDCCH) signal including a reserved bit (a TA groupindicator) indicating at least one TA group; receiving a Medium AccessControl (MAC) message including at least one TA value for the at leastone TA group; and transmitting an uplink signal by applying the at leastone TA value to the at least one TA group indicated by the reserved bit,wherein each of the at least one TA group includes at least one PrimaryCell (PCell).
 2. The method according to claim 1, wherein each of the atleast one TA group has a different Uplink (UL)-Downlink (DL)configuration.
 3. The method according to claim 1, wherein each of theat least one PCell has a different UL-DL configuration.
 4. The methodaccording to claim 1, wherein the at least one TA group includes aSecondary Cell (SCell) related to the at least one PCell.
 5. The methodaccording to claim 4, wherein the at least one TA value is appliedcommonly to one or more serving cells of the at least one TA groupcorresponding to the at least one TA value.
 6. A method for adjusting atransmission timing for at least one Timing Advance (TA) group in awireless access system supporting Carrier Aggregation (CA), the methodcomprising: transmitting a Physical Downlink Control Channel (PDCCH)signal including a reserved bit (a TA group indicator) indicating atleast one TA group; transmitting a Medium Access Control (MAC) messageincluding at least one TA value for the at least one TA group; andreceiving an uplink signal that is transmitted by applying the at leastone TA value to the at least one TA group indicated by the reserved bit,wherein each of the at least one TA group includes at least one PrimaryCell (PCell).
 7. The method according to claim 6, wherein each of the atleast one TA group has a different Uplink (UL)-Downlink (DL)configuration.
 8. The method according to claim 6, wherein each of theat least one PCell has a different UL-DL configuration.
 9. The methodaccording to claim 6, wherein the at least one TA group includes aSecondary Cell (SCell) related to the at least one PCell.
 10. The methodaccording to claim 9, wherein the at least one TA value is appliedcommonly to one or more serving cells of the at least one TA groupcorresponding to the at least one TA value.
 11. A terminal for adjustinga transmission timing for at least one Timing Advance (TA) group in awireless access system supporting Carrier Aggregation (CA), the terminalcomprising: a transmission module; a reception module; and a processorconfigured to adjust the transmission timing, wherein the terminalreceives a Physical Downlink Control Channel (PDCCH) signal including areserved bit (a TA group indicator) indicating at least one TA groupthrough the reception module, receives a Medium Access Control (MAC)message including at least one TA value for the at least one TA groupthrough the reception module, and transmits an uplink signal by applyingthe at least one TA value to the at least one TA group indicated by thereserved bit through the processor, and wherein each of the at least oneTA group includes at least one Primary Cell (PCell).
 12. The terminalaccording to claim 11, wherein each of the at least one TA group has adifferent Uplink (UL)-Downlink (DL) configuration.
 13. The terminalaccording to claim 11, wherein each of the at least one PCell has adifferent UL-DL configuration.
 14. The terminal according to claim 11,wherein the at least one TA group includes a Secondary Cell (SCell)related to the at least one PCell.
 15. The terminal according to claim14, wherein the at least one TA value is applied commonly to one or moreserving cells of the at least one TA group corresponding to the at leastone TA value.